This application claims the priority benefit of Taiwan application serial no. 91120043, filed Sep. 3, 2002.
1. Field of the Invention
The invention relates in general to a package for an organic electroluminescent (EL) device, and more particularly, to a package for an organic electroluminescent device using an ultra-violet (UV) curing resin and a thermal curing resin as a sealant.
2. Related Art of the Invention
The basic structure of an organic electroluminescent device includes an anode, a cathode, and an organic thin film with luminescent property sandwiched in between. By applying an appropriate bias, the holes are injected from the anode, and the electrons are injected from the cathode. The application of the external bias generates an external potential to provide mobility of the carriers, that is, the holes and electrons in the thin film. As a result, the carriers recombine and generate energy. A part of the energy released by the recombination of electron and hole stimulates the luminescent molecules to a single excited state. When the excited luminescent molecules release energy and return to the ground state, a certain proportion of the energy is released to generate photons which produce illumination. This is the mechanism for electroluminescence. Having the properties of self-luminescence, wide viewing angle, high response speed, low driving voltage and full color, the organic electroluminescent devices have become the leading technology of flat panel displays for the next generation.
As the operation stability and endurance of the electroluminescent device is directly affected by the package thereof, the package is expected to have promising permeability and adhesion. The metal thin film (electrode) is easily deteriorated by moisture and oxygen, and the organic electroluminescent is easily photodegraded. Further, oxygen provides the path for forming radicals in the luminescent layer. The radicals include carbonyl that reduces the luminescent efficiency of the luminescence layer and breaks the molecular bonds to shorten the device lifetime. Therefore, absorbent is incorporated in the device, or one or multiple layers of protection are coated on the device to absorb or to prevent moisture and oxygen from permeating the package.
FIG. 1 shows a conventional package for an organic electroluminescent device. Referring to FIG. 1, the conventional package for the organic electroluminescent device includes a substrate 100, an organic electroluminescent device 102, a cover plate 104, and a sealant 108. The organic electroluminescent device is mounted on the substrate 100. The cover plate 104 is connected to the substrate 100 via the sealant 108 to enclose the organic electroluminescent device 102. The sealant 108 includes a frame-like resin surrounding the organic electroluminescent device 102. The cover plate 104 has a recess 104a to accommodate an absorbent 106 therein. The absorbent 106 prevents moisture and oxygen from permeating into the package of the organic electroluminescent device.
In the conventional package of the organic electroluminescent device, the sealant 108 is typically a UV curing resin or a thermal curing resin. When the UV curing resin is used for the sealant 108, the package has very good permeability. However, the adhesion between the substrate 100 and the cover plate 104 is not ideal. When the thermal curing resin is used for the sealant 108, proper adhesion is obtained; however, the permeability is poor. Therefore, neither the UV curing resin or the thermal curing resin can provide sufficient permeability and adhesion at the same time.
The present invention provides a package for an organic electroluminescent device with sufficient permeability and adhesion.
The package of the organic electroluminescent device provided by the present invention includes a substrate, an organic electroluminescent device, a sealant, and a cover plate. The organic electroluminescent device and the sealant are disposed on the substrate, while the sealant includes a frame-like resin surrounding the organic electroluminescent device. The sealant includes both a UV curing resin and a thermal curing resin. The cover plate is located over the substrate and connected thereto via the sealant, such that the organic electroluminescent device is enclosed thereby.
In one embodiment of the present invention, the disposition of the UV curing resin and the thermal curing resin of the sealant includes: (1) the UV curing resin is located at the side near the organic electroluminescent device, while the thermal curing resin is located at a distal side of the organic electroluminescent device; (2) the thermal curing resin is located at the side near the organic electroluminescent device, while the UV curing resin is located at a distal side of the organic electroluminescent device; (3) the thermal curing resin is covered by the UV curing resin; and (4) the UV curing resin is covered by the thermal curing resin.
In one embodiment of the present invention, an absorbent is further included in the cover plate. The absorbent is not in contact with the organic electroluminescent device. A recess can be made in the cover plate to accommodate the absorbent, such that the thickness of the whole package can be reduced.